This is a short worksheet that guides students through simple metal lattices (SCP, CCP, HCP) and how filling holes in these lattices results in ionic lattices (NaCl, CsCl, fluorite, etc.).
The worksheet was used as an in-class activity after students had read about the material in the text. This activity is probably suitable for first-year students, though I used it with juniors/seniors.
Students will be able to do the following:
for simple lattices:
draw the lattice
determine how many atoms per cell
determine the coordination number, CN, of an atom
locate common holes and describe their CN
calculate the % of space filled up by the atoms
For ionic solids:
draw the lattice and count the number of ions in the cell
relate to a simple lattice by hole-filling
determine the # and CN of both cations and anions
none, though a box of pennies or marbles or ping pong balls might be helpful to visualize closest packing. Having models or computer models would have been helpful to show on a screen at the front of the room. rotatable cif files would be especially good, and next time I do this I will prepare cif files or crystalmaker files and upload them here.
This was a bit too long for a 50-minute class period but students finished it up at home. The students who had spent the time reading the book before class definitely did better on the exercise than those who were clearly doing it for the first time in class. Students struggled a bit with the geometry/trig calculations.
Were I to do this again, I would have 3-d rotatable structures available (cif files or crystalmaker files) to help students with the visualization.
I walked through the classroom and guided the students as they worked in pairs or groups of three. All the answers were in prior assigned reading from their text so if they were confused, they had that to look at later.
Some students had trouble seeing some of the holes in the simple lattices, so it was helpful that I was walking around to show them the holes. It was good to have students work together becasue some students were able to see the holes in the geometries and help their partners.